CAMBRIAN BRACHIOPODA WALCOTT I05 



EOORTHIS NEWBERRYI, new species 



Plate io, Figures 6 and 6a 



Shell transversely subelliptical, with the cardinal extremities ob- 

 tusely angular ; valves moderately convex, with the hinge line a 

 little shorter than the greatest width of the valves. The only ventral 

 valve in the collection showing a mesial fold is a small exfoliated 

 shell that is somewhat doubtfully referred to the species. Two of 

 the larger valves in the collection have the posterior margin extended 

 beyond the hinge line, with a short incurved beak ; a broad, shallow 

 median sinus begins in front of the umbo and widens to nearly one- 

 third of the width of the valve at the frontal margin. On a shell 

 5 mm. in length the sinus is very shallow ; area unknown. The 

 dorsal valve is almost uniformly convex and without a mesial sinus 

 or fold ; the front margin arches upward a little to provide for the 

 extension of the margin of the ventral valve caused by its broad 

 median sinus ; beak minute and marginal ; area unknown. 



Surface marked by concentric lines and ridges of growth and 

 small, rounded, radiating ribs with two or three smaller ribs between 

 each two larger ridges. The shell structure is fibrous and im- 

 punctate, as far as can be determined from the material available 

 for study. The largest ventral valve has a length of 14 mm. ; width, 

 18 mm. A dorsal valve 15 mm. in length has a width of 18 mm. 



Observations. — In form this species resembles some species of 

 Eoorthis rcmnicha (N. H. Winchell) [1886, p. 317], but in surface 

 characters it is quite unlike any of them. 



Formation and Locality. — Upper Cambrian: About 1,100 feet 



(335.3 m.) above the top of the Middle Cambrian and 125 feet 



(38.1 m.) below the Lower Ordovician, in the limestone of the St. 

 Charles formation of the Blacksmith Fork Section, about 7 miles 



(11.27 km.) above the mouth of Blacksmith Fork and 14 miles 



(22.54 km.) east of Hyrum, Cache County, Utah. 



EOORTHIS THYONE, new species 



Plate 10, Figures 7 and ya 



In outline and size this species resembles Eoorthis wichitensis 

 (Walcott) [1905a, p. 271], but in its sharp, uniform, radiating ribs 

 it differs from that and other species having a somewhat similar 

 outline. The ribs radiate from the beak and increase in number by 

 interpolation of new ribs at irregular distances from the beak. Noth- 

 ing is known of the area of either valve. A cast of the interior of a 

 dorsal valve shows rather large muscle scars. 



